The Experts below are selected from a list of 231 Experts worldwide ranked by ideXlab platform
Gray A. Williams - One of the best experts on this subject based on the ideXlab platform.
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intraspecific variation in foraging behaviour influence of shore height on temporal organization of activity in the chiton acanthopleura japonica
Marine Ecology Progress Series, 2006Co-Authors: Jasmine S S Ng, Gray A. WilliamsAbstract:The chiton Acanthopleura japonica has a wide vertical distribution on moderately exposed Hong Kong shores, and it shows limited seasonal vertical migration. Observations revealed that chitons were active while awash on ebbing or flooding tides during both day- and night-time, but they were inactive in refuges at their resting shore heights when conditions were unfavourable. The most intense activity was always associated with awash periods, but the timing of activity peaks and percentage activity varied between seasons, tidal conditions and the shore height individuals'occupied. Activity periods were longer in summer than winter, but varied from day to day, depending on weather conditions such as wind speed and hours of sunshine. Duration of activity also varied with shore height; chitons living in the high-shore remaining active for nearly twice as long as those lower on the shore. Laboratory studies showed that activity Was controlled by a circalunidian Endogenous Rhythm, but can be overridden by exogenous, environmental factors, such as wave splash. Therefore, the temporal organization of activity in A. japonica is controlled by both exogenous and Endogenous mechanisms, of which the timing and duration of the awash phase of the tide appears to be the dominant controlling factor. To optimize foraging success, individuals exhibit a continuum of foraging strategies determined by season and the shore height they occupy, resulting in intraspecific variability in the duration and timing of activity.
Olivier Pierrefiche - One of the best experts on this subject based on the ideXlab platform.
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ionic currents and Endogenous Rhythm generation in the pre botzinger complex modelling and in vitro studies
Advances in Experimental Medicine and Biology, 2004Co-Authors: Ilya A Rybak, Natalia A Shevtsova, Julian F R Paton, Walter M St John, Olivier PierreficheAbstract:The pre-Botzinger complex (pBC), a small area in the rostroventrolateral medulla, has been suggested to represent a “kernel” of the mammalian respiratory network1, 2, 3, 4, 5. The in vitro preparations from neonatal rodents containing this area can, under certain experimental conditions, generate an intrinsic Rhythmic activity4,5. This activity does not require inhibitory neurotransmission6 and, therefore, is likely to be generated by a population of pacemaker neurons in the pBC1, 2, 3, 4, 5. At the same time, the “decrementing” discharge pattern of Rhythmic activity in the pBC recorded in vitro differs from the pattern of respiratory discharges observed under normal conditions in vivo (“eupnoea”) and is similar to gasping pattern7, 8. In order to establish possible relationships of the intrinsic Rhythmic activity in the pBC to the respiratory Rhythmogenesis in vivo, it is important to analyse the conditions in which this activity occurs in vitro and to compare these conditions with the Rhythmogenic conditions during eupnoea and gasping in vivo. According to the preliminary modelling studies9, the in vitro Rhythmic activity in the pBC may be dependent on a relative expression of the voltage-gated potassium and persistent sodium currents in pBC neurons. Here we present the results of our combined modelling and in vitro studies performed to test this modelling prediction. Our studies focused on the involvement of the potassium and persistent sodium currents in the Endogenous Rhythmic activity in the pBC in vitro and on the possible relation of this activity to the genesis of the respiratory oscillations in vivo.
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Endogenous Rhythm generation in the pre botzinger complex and ionic currents modelling and in vitro studies
European Journal of Neuroscience, 2003Co-Authors: Ilya A Rybak, Natalia A Shevtsova, Walter M Stjohn, Julian F R Paton, Olivier PierreficheAbstract:The pre-Botzinger complex is a small region in the mammalian brainstem involved in generation of the respiratory Rhythm. As shown in vitro, this region, under certain conditions, can generate Endogenous Rhythmic bursting activity. Our investigation focused on the conditions that may induce this bursting behaviour. A computational model of a population of pacemaker neurons in the pre-Botzinger complex was developed and analysed. Each neuron was modelled in the Hodgkin-Huxley style and included persistent sodium and delayed-rectifier potassium currents. We found that the firing behaviour of the model strongly depended on the expression of these currents. Specifically, bursting in the model could be induced by a suppression of delayed-rectifier potassium current (either directly or via an increase in extracellular potassium concentration, (K þ )o) or by an augmentation of persistent sodium current. To test our modelling predictions, we recorded Endogenous population activity of the pre-Botzinger complex and activity of the hypoglossal (XII) nerve from in vitro transverse brainstem slices (700mm) of neonatal rats (P0-P4). Rhythmic activity was absent at 3 mM (K þ )o but could be triggered by either the elevation of (K þ )o to 5-7 mM or application of potassium current blockers (4-AP, 50-200mM, or TEA, 2 or 4 mM), or by blocking aerobic metabolism with NaCN (2 mM). This Rhythmic activity could be abolished by the persistent sodium current blocker riluzole (25 or 50mM). These findings are discussed in the context of the role of Endogenous bursting activity in the respiratory Rhythm generation in vivo vs. in vitro and during normal breathing in vivo vs. gasping.
Benoît Malpaux - One of the best experts on this subject based on the ideXlab platform.
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Endogenous circannual Rhythm in lh secretion insight from signal analysis coupled with mathematical modelling
arXiv: Dynamical Systems, 2009Co-Authors: Alexandre Vidal, Claire Medigue, Benoît Malpaux, Frédérique ClémentAbstract:In sheep as in many vertebrates, the seasonal pattern of reproduction is timed by the annual photoperiodic cycle, characterized by seasonal changes in the daylength. The photoperiodic information is translated into a circadian profile of melatonin secretion. After multiple neuronal relays (within the hypothalamus), melatonin impacts GnRH (gonadotrophin releasing hormone) secretion that in turn controls ovarian cyclicity. The pattern of GnRH secretion is mirrored into that of LH (luteinizing hormone) secretion, whose plasmatic level can be easily measured. We addressed the question of whether there exists an Endogenous circannual Rhythm in a tropical sheep population that exhibits clear seasonal ovarian activity when ewes are subjected to temperate latitudes. We based our analysis on LH time series collected in the course of 3 years from ewes subjected to a constant photoperiodic regime. Due to intra- and inter- animal variability and unequal sampling times, the existence of an Endogenous Rhythm is not straightforward. We have used time-frequency signal processing methods to extract hidden Rhythms from the data. To further investigate the LF (low frequency) and HF (high frequency) components of the signals, we have designed a mathematical model of LH plasmatic level accounting for the effect of experimental sampling times. The model enables us to confirm the existence of an Endogenous circannual Rhythm, to investigate the action mechanism of photoperiod on the pulsatile pattern of LH secretion (control of the interpulse interval) and to conclude that the HF component is mainly due to the experimental sampling protocol.
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the Endogenous Rhythm of plasma melatonin and its regulation by light in the highveld mole rat cryptomys hottentotus pretoriae a microphthalmic seasonally breeding rodent
Journal of Pineal Research, 2004Co-Authors: Gundula H Gutjahr, Benoît Malpaux, Janse L Van Rensburg, T A Richter, Nigel C BennettAbstract:: The day- and night-time levels of plasma melatonin were measured in adult male and female highveld mole-rats, Cryptomys hottentotus pretoriae. This study aimed to assess whether melatonin secretion in this nocturnal, strictly subterranean but seasonally breeding rodent has a day-night Rhythm and whether that Rhythm is circadian and can be modified by photoperiod. In experiment 1, a day-night Rhythm of plasma melatonin was found in all animals housed on a 12L:12D schedule, with significantly higher concentrations in the dark (D) compared with the light (L) phase. The increment of plasma melatonin concentration at night was the same on days 1 and 2 for animals in the control group and animals transferred to constant dark. The animals transferred to constant light substantially reduced the amplitude of the melatonin Rhythm on day 2. This suggests that the Endogenous melatonin Rhythm in C. h. pretoriae has a circadian pattern, which can be synchronized by photoperiod and inhibited by exposure to light at night. In experiment 2, the concentration of plasma melatonin in animals kept under 14L:10D (long day, LD) conditions differed significantly from animals on 10L:14D (short day, SD). This finding supports the notion that C. h. pretoriae is sensitive to changes in day length.
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control of the circannual Rhythm of reproduction by melatonin in the ewe
Brain Research Bulletin, 1997Co-Authors: Benoît Malpaux, Jeanclaude Thiery, Donal C Skinner, Catherine Viguie, Philippe ChemineauAbstract:Annual variations in day length are responsible for seasonal changes in reproductive activity in sheep. However, in constant photoperiodic conditions, ewes express an Endogenous Rhythm characterized by alternations of reproductive activity and quiescence that are not synchronized among animals. Thus, the main role of photoperiod in the natural environment appears to be the synchronization of this Endogenous Rhythm. Photoperiodic information is processed through a complex nervous and endocrine pathway to modulate reproductive activity. Light information perceived at the level of the retina is transformed through neural processing into an endocrine signal by the pineal gland: the nocturnal increase in melatonin release. Recent studies strongly suggest that melatonin has a hypothalamic target to modulate the reproductive neuroendocrine axis. Most LHRH perikarya are located in the preoptic area, but this region is devoid of melatonin receptors, and microimplants of melatonin placed in the preoptic area do not effect LHRH release. Thus, melatonin influences LHRH neurones indirectly and must involve interneurons. Good evidence now exists to demonstrate that a population of dopaminergic neurons with axons projecting to the median eminence is one of these interneurons.
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photoperiodic requirements for timing onset and duration of the breeding season of the ewe synchronization of an Endogenous Rhythm of reproduction
Journal of Comparative Physiology A-neuroethology Sensory Neural and Behavioral Physiology, 1990Co-Authors: Nancy L Wayne, Benoît Malpaux, Fred J KarschAbstract:A study was conducted to test the hypothesis that different portions of the annual photoperiodic cycle play different roles in timing the breeding season of the ewe, Ovis aries, an animal in which an Endogenous Rhythm generates the seasonal reproductive transitions. Adult female sheep were pinealectomized to disrupt transduction of photoperiodic cues at 4 times of the year (summer and winter solstices, vernal and autumnal equinoxes), and the effects on seasonal reproductive neuroendocrine activity were evaluated. Time of pinealectomy greatly influenced the subsequent seasonal reproductive cycle such that the following inferences are possible. Lengthening days between the winter and summer solstices synchronize reproductive onset to the appropriate time of year. The relatively long days around the summer solstice act to suppress reproductive activity and forestall the start of the breeding season until late summer/early autumn. The shortening days between the summer solstice and autumnal equinox maintain a normal intensity and duration of reproductive neuroendocrine induction during the impending breeding season. However, the shortening days between the autumnal equinox and winter solstice (i.e., after breeding season onset) do not appear to play a critical role in maintaining the breeding season of that year, but may provide important cues for timing the breeding season of the following year.
Gilles Van Luijtelaar - One of the best experts on this subject based on the ideXlab platform.
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Endogenous Rhythm of absence epilepsy relationship with general motor activity and sleep wake states
Epilepsy Research, 2011Co-Authors: Magdalena K Smyk, A M L Coenen, M H Lewandowski, Gilles Van LuijtelaarAbstract:Summary The Rhythms of spontaneously occurring seizures (spike-wave discharges, SWD) and motor activity, as well as the relationship between SWD and sleep–wake states were investigated in the WAG/Rij rat model of absence epilepsy. In order to establish whether SWD are controlled by external (Zeitgebers) or by Endogenous factors such as circadian influences or the state of vigilance, the study was performed in entrained and constant dim light conditions. EEG and motor activity were recorded in the 12:12 light–dark cycle and in constant dim light conditions. Circadian Rhythmicity was found both for motor activity and the occurrence of SWD in conditions of entrainment. In constant dim light conditions also circadian Rhythms emerged, however, the change in circadian parameters was opposite for the Rhythm of SWD and motor activity. SWD were preceded mostly by passive wakefulness and by slow-wave sleep in both experimental conditions. It can be concluded that the Rhythm of SWD seems to be generated and controlled by an Endogenous mechanism distinct from that which controls the Rhythm of motor activity. The relationship between SWD and sleep–wake states preceding their occurrences appeared to be unchanged, suggesting that the mechanism of generation of SWD is independent of the circadian timing system.
Jasmine S S Ng - One of the best experts on this subject based on the ideXlab platform.
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intraspecific variation in foraging behaviour influence of shore height on temporal organization of activity in the chiton acanthopleura japonica
Marine Ecology Progress Series, 2006Co-Authors: Jasmine S S Ng, Gray A. WilliamsAbstract:The chiton Acanthopleura japonica has a wide vertical distribution on moderately exposed Hong Kong shores, and it shows limited seasonal vertical migration. Observations revealed that chitons were active while awash on ebbing or flooding tides during both day- and night-time, but they were inactive in refuges at their resting shore heights when conditions were unfavourable. The most intense activity was always associated with awash periods, but the timing of activity peaks and percentage activity varied between seasons, tidal conditions and the shore height individuals'occupied. Activity periods were longer in summer than winter, but varied from day to day, depending on weather conditions such as wind speed and hours of sunshine. Duration of activity also varied with shore height; chitons living in the high-shore remaining active for nearly twice as long as those lower on the shore. Laboratory studies showed that activity Was controlled by a circalunidian Endogenous Rhythm, but can be overridden by exogenous, environmental factors, such as wave splash. Therefore, the temporal organization of activity in A. japonica is controlled by both exogenous and Endogenous mechanisms, of which the timing and duration of the awash phase of the tide appears to be the dominant controlling factor. To optimize foraging success, individuals exhibit a continuum of foraging strategies determined by season and the shore height they occupy, resulting in intraspecific variability in the duration and timing of activity.